(1) Field of the Invention
This invention relates to image reading apparatuses, which read images on an original copy as an electric data using image sensors comprising light receiving elements one-dimensionally arranged, such as scanners, faxes, copiers and complex machines of these.
(2) Background Art
Image reading apparatuses which read images on the original copy as electric data using image sensors comprising light receiving elements one-dimensionally arranged are already known as scanners, faxes, copiers and complex machines of these.
There are various ways how to read desired image data. The selection of the way to be used depends on the use of the read image or conditions at the reading process. In some cases, high precision is required for photo images despite of increase in the data volume. In other cases the data volume of the read image needs to be reduced for a data transmission by FAX rather than keeping the precision. Sometimes both of the precision and the data volume should modestly be maintained.
Conventional apparatuses can change precisions and data volumes by outputting the data of read image with the resolution increased or decreased in accordance with the data in use.
In case of having a text image read using an OCR (Optical Character Reader), certain degree of resolution is necessary for OCR recognition, but the dynamic range can be low because the image signals will be digitalized by determining the signal level with a threshold. The reading time should be more concerned and should be shorter. Often the number of pages to go through the reading process is large. In this kind of case, the priority should be given to the speed of image reading.
In another case, a resolution is inevitably set low because of the limit to a data volume of, for instance, a photo image though reproduction of the image is required as much as possible. In this case, the priority should be given to the image quality.
However, none of image reading apparatus has been able to read images at the same resolution with some changes in conditions, such as reading speed, depending on the situation. The image data for OCR mentioned above outputs the data read by image sensors after digitalizing it. The output is still done through image sensors, and the reading time is not significantly different in comparison with reading images with a gradation.
As described above, known image reading apparatuses do not fulfill demands of users who sometimes need quality oriented image reading and other times speed oriented image reading with the same condition of the resolution.
The present invention is to concern these matters, and its object is to provide an image reading apparatus which is capable of choosing a reading manner from a quality oriented image reading and a speed oriented image reading, even when the images have the same condition of resolution.